Author Topic: 1960 A7 Shooting Star Sprocket Sizes  (Read 674 times)

Offline sheffield steel

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1960 A7 Shooting Star Sprocket Sizes
« on: 12.04. 2020 20:02 »
Hi All
I’m sure this must have been discussed previously but I can’t seem to find any advice. I have a 1960 A7 Shooting Star, it has a rebuild engine with many uprated parts which runs great, but performance wise is pretty much standard. I’m running what I believe to be standard size sprockets (19/42) which seems to give great performance from a standing start but at 50mph or so it’s all out of puff. I’ve tried a 20T front sprocket which appeared to make things very sluggish (unless I failed to give it adequate chance to prove itself). Is there a better gear ratio available or am I just expecting too much from the old girl?
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Offline berger

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #1 on: 12.04. 2020 21:09 »
confused, is timing set up correctly, what size crank sprocket is on it, mine fly's with 20 engine 19 or 20 gearbox, didn't fly with a 23 engine  *whistle*
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Offline Swarfcut

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #2 on: 13.04. 2020 08:41 »
Bergs. You and me both.  '54-62  SS as standard has 18 teeth on the crank, 43 on the standard clutch drum.  Usual 19 on the box, rear cog is 42 teeth.

  SS..... We don't know enough of the build spec of this bike to offer an answer, but as a first step checking the basics is a must. "Out of puff" is a bit subjective, but the wrong carb set up and a simple blocked air filter is a first place to look.

 Swarfy.
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Offline sheffield steel

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #3 on: 13.04. 2020 16:23 »
Thanks for you responses.
I fairly confident that the timing is correct and there’s no air filter fitted so that definitely isn’t the problem!
There seems to be some confusion on the standard sprocket size in the primary which I’m now suspecting is the issue. I’m running 18 engine, 43 clutch, 19 front sprocket and 42 rear sprocket. The general consensus seems to be that a 19, 20 or 21 might be more suitable on the crank though?
Bike is a 1960 A7 S/S swing arm.
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Online JulianS

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #4 on: 13.04. 2020 17:01 »
Your sprockets are as the book says. Below from the owners manual.
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Offline sheffield steel

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #5 on: 13.04. 2020 19:21 »
The book I have also shows those sizes which are what I’m running. However the general opinion in a long discussion on the BSA Singles & Twins page on Facebook is that I should be running at least 20T on the engine if not 21T. They all seem to think that 18T is for sidecar work.
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Online JulianS

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #6 on: 13.04. 2020 19:54 »
You say the bike out of puff at 50 mph.

50 equates to about 3500 rpm on the BSA specified sprockets. So it seems that something is inhibiting the bike from reving. Fitting a larger sprocket will not help it rev.

Fit too large a sprocket and the bike will be faster in third than in top will be much less flexible and accelerstion will be slower.

You can see from the page I posted earlier what the factory recommended sprockets for sidecar are.


 
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Offline chaterlea25

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #7 on: 13.04. 2020 22:51 »
Hi All,
My opinion is that the original gearing was suitable for the road speeds of the 50's and 60's

For today's higher road speeds the gearing can be upped to provide a more relaxed ride
Its been a very long time since I rode an A7SS, but remember winding it on and seeing just shy of the magic "ton" on the speedo  *eek* (I have no idea how correct it was though ) 

My own SR 650 will rev out with a 23/43, 19 /42 gearing  *smile*

I think there must be something up with Sheffield's A7  *????*

John
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Offline Rocket Racer

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #8 on: 14.04. 2020 00:54 »
How restrictive are those mufflers?
 gearing a bike up doesnt make it faster, and can result in a lot more use of third gear and the bike not ever getting on the cam in top.
As mentioned we have no idea whats in this motor but through the gears does it appear eager and rev or feel flat?
On my (race) RR I keep it to 6500 but have to watch the tach as it'll keep revving well into the 7's, these engines if not constipated should be very willing.
I have a stock cooking plunger B33 and that will never go past 5000 but is strong as an ox up to near 80mph (runs a19T engine sprocket)     
Perhaps the motors still tight?
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A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline berger

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #9 on: 14.04. 2020 11:56 »
I have to agree with RR about a tight motor , I knew with mine after rebuild when it had reached its loose stage, it proper took off and I hit 7000 in first and second then thought don't be a pillock *bash*
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Offline sheffield steel

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #10 on: 14.04. 2020 19:55 »
Thanks all for the suggestions
The bottom end was rebuilt by SRM a few years back but I can’t be doing more than a few hundred miles a year. Bottom engine has bearing conversion and billet rods etc but essentially is standard performance wise. Head has been overhauled but again it’s standard. When I’m riding it the engine feels great, revs nice and freely and pulls well but just seems to rev out at about 50/60 tops. It certainly feels like a gearing problem to me rather than an engine or timing issue but I’m no expert with these engines.

I do want to strip the carb and check jet sizes etc though.
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Offline UKlittleguns

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #11 on: 16.04. 2020 18:21 »
Hi Sheffield,

I'm very new to motorbike engines.  But, in times past I spent many years with performance car engines.  I saw a great many that were over ported on the inlet side.  Chuck away the standard air filters, fit twin Webbers and air horns. They looked good, sounded good, but bogged down at speed.  There was not enough depression on the carbs to drag the fuel through at speed.  You say you're not running an air filter.  Just might be worth a try.

Regards

Len
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Offline Rocket Racer

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #12 on: 16.04. 2020 21:31 »
When I’m riding it the engine feels great, revs nice and freely and pulls well but just seems to rev out at about 50/60 tops. It certainly feels like a gearing problem to me ...

When you say rev out, is she fair howling? you want to take pity on the motor, she cant give any more... I'm more familiar with the larger motors although have ridden a mates star twin and that is a real smoothie, purrs along at the speeds you mention effortlessly all day without showing a sweat. When I had a super rocket in road trim that was happy at 60/70mph open road cruising and not revved out but was on song with more at hand for passing. For road use these bikes are not naturally tapped out as we want to get home, they do like revs and eddie dow once quoted the safe continuous red line at 6800.

I certainly am not a fan of over gearing, you put more loads through the engine and reduce the oil pressure. Once they are warmed up they are happy to buzz along all day. It doesnt do them any harm and the hotter cams like more than 4000 on the clock and sing at six.
There are many reasons this engine could be a bit constipated, tightness, too big a carb or incorrect jetting, too restrictive mufflers. But not I would expect gearing.
I would expect you would need to be on sidecar gearing to rev out at 60mph  or be on a c11 (they do run out of steam at 50!).
My zb33 absolutely barks (the exhaust note hardens up) at speeds over 60mph but its practically still only doing around 4000 odd (guess) as can be wound out to close to 80mph at which point she has gone flat powerwise (being around 5000) being on cooking cams.

But if you think its buzzing too hard and has nothing left, try amending the gearing by all means, its easy to do. Might though be worth doing some maths on what your current 60mph is in RPM. Its easy enough to do. You should be able to do that speed in third.
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A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline Rocket Racer

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #13 on: 16.04. 2020 23:01 »
with an 18 T you should be able to pull around 90mph
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A good rider periodically checks all nuts and bolts with a spanner to see that they are tight - Instruction Manual for BSA B series, p46, para 2.
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Offline berger

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Re: 1960 A7 Shooting Star Sprocket Sizes
« Reply #14 on: 17.04. 2020 00:11 »
that's interesting RR what is it with 20 -43 19 -42 I think mine hit the ton at about 6000, busy listening to engine  flat on tank and watching for the magic signal
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